Abstract

Sulfur accelerates coarsening of Ag nanoislands on Ag(100) at 300 K, and this effect is enhanced with increasing sulfur coverage over a range spanning a few hundredths of a monolayer, to nearly 0.25 monolayers. We propose that acceleration of coarsening in this system is tied to the formation of AgS2clusters primarily at step edges. These clusters can transport Ag more efficiently than can Ag adatoms (due to a lower diffusion barrier and comparable formation energy). The mobility of isolated sulfur on Ag(100) is very low so that formation of the complex is kinetically limited at low sulfur coverages, and thus enhancement is minimal. However, higher sulfur coverages force the population of sites adjacent to step edges, so that formation of the cluster is no longer limited by diffusion of sulfur across terraces. Sulfur exerts a much weaker effect on the rate of coarsening on Ag(100) than it does on Ag(111). This is consistent with theory, which shows that the difference between the total energy barrier for coarsening with and without sulfur is also much smaller on Ag(100) than on Ag(111).

The experimental component of this work was supported by National Science Foundation (NSF) Grant No. CHE-1111500. The theoretical component (D.J.L.'s contribution) was supported by the Division of Chemical Sciences, Basic Energy Sciences, (U.S.) Department of Energy (USDOE). The work was performed at Ames Laboratory, which is operated for the USDOE by Iowa State University under Contract No. DE-AC02-07CH11358. We thank J. W. Evans for a useful critique of this work.